The characteristics and mechanism of conduction/set process in TiN∕ZnO∕Pt-based resistance random access memory devices with stable and reproducible nanosecond bipolar switching behavior were studied. The dependencies of memory behavior on cell area, operating temperature, and frequency indicate that the conduction mechanism in low-resistance states is due to electrons hopping through filament paths. We also identify that the set process is essentially equivalent to a soft dielectric breakdown associated with a polarization effect caused by the migration of space charges under a low electric field stress. The generation/recovery of oxygen vacancies and nonlattice oxygen ions play a critical role in resistance switching.

An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.

Oxygen vacancy (VO) plays the critical role for resistive switching in transition metal oxide resistive random access memory (RRAM). First principles calculation is performed to study the impact of metallic ion (Al, Ti, or La) doping in ZrO2 on the behaviors of VO, including defect energy level and formation energy (Evf). Trivalent dopant (Al or La) significantly reduces Evf. Based on the calculated results, ZrO2-based RRAM devices are designed to control the formation of VO, and improved resistive switching uniformity is demonstrated in experiments.